net: ethtool: add ring parameter filtering

While the devmem is running, the tcp-data-split and
hds-thresh configuration should not be changed.
If user tries to change tcp-data-split and threshold value while the
devmem is running, it fails and shows extack message.

Reviewed-by: Jakub Kicinski <kuba@kernel.org>
Tested-by: Stanislav Fomichev <sdf@fomichev.me>
Reviewed-by: Mina Almasry <almasrymina@google.com>
Signed-off-by: Taehee Yoo <ap420073@gmail.com>
Link: https://patch.msgid.link/20250114142852.3364986-5-ap420073@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

net/ethtool/rings.c

@@ -252,6 +252,19 @@ ethnl_set_rings(struct ethnl_req_info *req_info, struct genl_info *info)
 		return -EINVAL;
 	}
 
+	if (dev_get_min_mp_channel_count(dev)) {
+		if (kernel_ringparam.tcp_data_split !=
+		    ETHTOOL_TCP_DATA_SPLIT_ENABLED) {
+			NL_SET_ERR_MSG(info->extack,
+				       "can't disable tcp-data-split while device has memory provider enabled");
+			return -EINVAL;
+		} else if (kernel_ringparam.hds_thresh) {
+			NL_SET_ERR_MSG(info->extack,
+				       "can't set non-zero hds_thresh while device is memory provider enabled");
+			return -EINVAL;
+		}
+	}
+
 	/* ensure new ring parameters are within limits */
 	if (ringparam.rx_pending > ringparam.rx_max_pending)
 		err_attr = tb[ETHTOOL_A_RINGS_RX];